UV-CURABLE BLOCK COPOLYMER COMPOSITION

Abstract: UV-curable block copolymer composition comprising: (a) 100 parts by weight of a block copolymer comprising at least one polymer block A derived from a monovinyl aromatic compound and at least one polymer block B derived from a conjugated diene, wherein: the content of monovinyl aromatic compound is in the range of from 5 to 50 % by weight based on the total weight of block copolymer; each block A has an apparent molecular weight in the range of from 1,000 to 50,000; and each block B has an apparent molecular weight in the range of from 10,000 to 250,000; and (b) 0.5-30 parts by weight of at least one photoinitiator, characterized in that the block copolymer is a multi-armed block copolymer and at least one photoinitiator is used containing a carbonyl group which is directly bonded to at least one aromatic ring structure.

Description: UV-CURABLE BLOCK COPOLYMER COMPOSITION The present invention relates to a UV-curable block copolymer composition. More specifically, the present invention relates to a UV-curable block copolymer composition for adhesives, sealants and coatings comprising an elastomeric block copolymer and at least one photoinitiator. From PCT application No. WO 88/01281 a radiation curable rubber-based pressure-sensitive adhesive composition is known comprising at least one elastomeric rubber-based adhesive and a polythiol as the cross-linking agent. This composition can be cured by exposure to either electron beam radiation or UV irradiation. In the latter case, the additional presence of a photoinitiator is required. The presence of a cross-linking agent, in particular a polythiol, is taught to be essential for obtaining a cured pressure-sensitive adhesive composition having good adhesion properties and elevated temperature shear. However, it would be attractive for economical and processing reasons to reduce the number of components and still obtain a cured adhesive composition having excellent properties, also at elevated temperatures. U.S. Patent No. 5,093,406 discloses a pressure-sensitive adhesive comprising a free radical cured product formed by e.g. UV curing of a mixture containing: (a) 15-60 parts by weight (pbw) of an unsaturated elastomer component, suitably comprising styrene-isoprene diblock and styrene-isoprene-styrene triblock copolymers, (b) 85-40 pbw of a hydrogenated styrene based tackifying resin, (c) 0-15 pbw of a reinforcing resin for the polystyrene endblock of the elastomer component, and (d) 0-10 pbw of a polythiol cross-linking agent. Although the presence of a polythiol cross-linking agent is left optional, it is clearly a preferred embodiment, which for instance becomes readily apparent from the working examples, where only compositions containing a polythiol cross-linking agent are described. Hence, the need for a UV-curable composition, which does not require the presence of a cross-linking agent for an effective curing and which can be suitably applied in e.g. hot melt adhesive compositions, still remains. Often, rubber-based hot melt adhesive, sealant and coating compositions which do not contain any cross-linking agent, need to be cured in an atmosphere containing as little oxygen as possible. Upon exposure to UV irradiation namely, the aliphatic double bonds present in the rubber will open thus forming free radicals. The various rubber polymer chains containing free radicals along the polymer chains interact with each other through said free radicals as a result of which the desired cross-linking is accomplished. However, the free radicals also readily react with oxygen to form peroxides. It will be appreciated that the formation of such peroxides seriously hampers the cross-linking reaction. Consequently, curing of rubber based compositions which do not contain any cross-linking agent is conveniently performed in an inert gas atmosphere, most suitably in a nitrogen atmosphere. It will be understood that the requirement of an oxygen-poor atmosphere seriously hampers the commercial development of UV curing of rubber-based hot melt adhesives, sealants and coatings which are free of cross-linking agent. It would therefore be advantageous if UV curing could be performed in an atmosphere, wherein oxygen is present in minor traces up to normal amounts, i.e. from about as little as 1 volume % to the normal value in air of about 21 volume %. From a commercial as well as an economical point of view it is highly attractive to operate in relatively oxygen rich atmospheres, as no expensive equipment and specific precautions are necessary to ensure an oxygen-free atmosphere. Hence, it is an object of the present invention to provide a block copolymer composition which can be effectively cured by exposure to UV radiation without using any cross-linking agent. In addition, it is an object of the present invention to provide a UV-curable hot melt adhesive, sealant or coating composition which does not require the presence of any cross-linking agent and which can be readily cured in an oxygen-containing atmosphere. Accordingly, the present invention relates to a UV-curable block copolymer composition comprising: (a) 100 parts by weight (pbw) of a block copolymer comprising at least one polymer block A derived from a monovinyl aromatic compound and at least one polymer block B derived from a conjugated diene, wherein: the content of monovinyl aromatic compound is in the range of from 5 to 50% by weight based on the total weight of block copolymer; each block A has an apparent molecular weight in the range of from 1,000 to 50,000; and each block B has an apparent molecular weight in the range of from 10,000 to 250,000; and (b) from 0.5 to 30 pbw, preferably from 5 to 20 pbw, of at least one photoinitiator, characterized in that the block copolymer is a multi-armed block copolymer and at least one photoinitiator is used containing a carbonyl group which is directly bonded to at least one aromatic ring structure. With the expression "apparent molecular weight" as used throughout this description, the molecular weight as determined by Gel Permeation Chromatography using polystyrene calibration standards is meant. The block copolymer to be suitably used as component (a) in the composition according to the present invention in principle may be any block copolymer meeting the above mentioned requirements. Suitable block copolymers then include symmetric multi-armed block copolymers having a structure according to any one of the general formulas (AB) X, (BA) X, (ABA) X, (BAB) X as well as asymmetric or symetric multi-armed block copolymers of the general formula (AB) (B) X with A and B as defined above, n representing an integer. p q of 2 or higher and preferably 2 to 20, and p and q representing an integer of 1 or higher and preferably of from 1 to 3 depending on the functionality of the coupling agent used, of which coupling agent the residue is represented by X. Common coupling agents are for instance divinyl benzene, silicon tetrachloride, gamma glycidoxy-propyl-trimethoxy-silane and dibromoethane. A preferred block copolymer has the general formula (AB) X with A and B as previously defined, n representing an integer in the range of from 3 to 20, preferably 4 to 12, and X representing a coupling agent residue, preferably the residue of divinyl benzene. The multi-armed block copolymers may be prepared by coupling living sequentially prepared intermediate polymer chains by using any conventional coupling techniques, such as e.g. disclosed in U.S. Patents Nos. 3,231,635; 3,431,323; 3,251,905; 3,390,207; 3,598,887 and 4,219,627. • The monovinyl aromatic compound may be selected from styrene, -methylstyrene, o-methylstyrene, p-methylstyrene, p-tert-butyl- styrene, 1,3-dimethy1styrene or mixtures thereof, of which styrene is most preferred. Suitable conjugated dienes to be used in the block copolymer of component (a) are 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene) , 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexa- diene or mixtures thereof, of which 1,3-butadiene, isoprene or mixtures thereof are the preferred monomers. Isoprene is most preferred. As already indicated supra, it is preferred that the block copolymer is a multi-armed styrene(S)-isoprene(I) or styrene- butadiene(B) block copolymer having a styrene content in the range of from 5 to 25% by weight. An example of a commercially available multi-armed S-I block copolymer is KRATON D-1320X (KRATON is a trade mark) . The photoinitiator component (b) in the block copolymer composition according to the present invention may be composed of one or a combination of two or more photoinitiators. In any event, at least one of the photoinitiators used must be a compound containing a carbonyl group which is directly bonded to at least one aromatic ring structure. It is preferred that this photoinitiator is selected from the group consisting of: (1) at least one benzophenone of the general formula (I) 1 8 wherein R to R independently represent hydrogen or an alkyl group having from 1 to 4 carbon atoms, preferably methyl, and 7 8 wherein R and/or R represent in addition alkoxy of 1 to 4 carbon atoms and wherein n has a value of 0, 1 or 2, optionally in combination with at least one tertiary amine, (2) at least one sulphur-containing carbonyl compound, wherein the carbonyl group is directly bound to at least one aromatic ring, preferably of the general formula II 9 10 11 wherein R , R , R each may represent hydrogen, alkyl of 1-4 carbon atoms or an alkylthio group, having 1 to 4 carbon atoms, and (3) mixtures of (1) and (2) . Examples of suitable compounds of category (1) are benzo¬ phenone, 2,4,6-trimeth lbenzophenone, 4-methylbenzophenone and an eutectic mixture of 2,4,6-trimethylbenzophenone and 4-methylbenzo- phenone (ESACURE TZT) and 2,2-dimethoxy-l,2-diphenylethan-l-one (IRGACURE 651) (ESACURE and IRGACURE are trade marks). These compounds may be employed in combination with tertiary amines, such as e.g. UVECRYL 7100 (UVECRYL is a trade mark). Category (2) embraces compounds such as e.g. 2-methyl-l- [4- (methylthio)phenyl] -2-morpholinopropanone-l, commercially available as IRGACURE 907 (IRGACURE is a trade mark). An example of suitable mixtures (category (3)) is a mixture of 15% by weight of a mixture of 2-isopropylthioxanthone and 4-isopropylthioxanthone, and 85% by weight of a mixture of 2,4,6- trimethylbenzophenone and 4-methylbenzophenone. This mixture is commercially available under the trade name ESACURE X15. Photoinitiators of any one of the above categories (1), (2) and (3) may also be used in combination with other photoinitiators, such as e.g. UVECRYL P115. Particularly useful is a combination of benzophenone and said UVECRYL P115. in a preferred embodiment of the present invention the photoinitiator is selected from the group consisting of (i) benzophenone, (ii) a mixture of benzophenone and a tertiary amine containing a carbonyl group which is directly bonded to at least one aromatic ring, and (iii) 2-methyl-l- [4-(methylthio)phenyl] -2- morpholinopropanone-1. Of these 2-methyl-l- [4-(methylthio)phenyl] - 2-morpholinopropanone-l is most preferred. The photoinitiator should be present in an amount of from 0.5 to 30 parts by weight per 100 parts by weight of block copolymer (phr) to ensure sufficient cross-linking upon exposure to UV irradiation. It is preferred that the photoinitiator is present in an amount of from 5 to 20 phr. The UV irradiation used for cross-linking the block copolymer composition of the present invention in principle may be any UV source having an output spectra showing one or more peaks at wavelengths between 200 and 500 nanometer (nm) . Particularly suitable UV sources are Fusion bulb lamps (Fusion is a trade mark) having output maxima at 260-270 nm, 320 nm and 360 nm ("H" bulb), at 350-390 nm ("D" bulb) or at 400-430 nm ("V" bulb). Combinations of these Fusion bulb lamps may also be used. H and D bulb lamps (linear power 300 W/inch) are particularly useful, while a combination of D bulb and H bulb can also be suitably applied. The exposure to UV irradiation may be performed by any known method. A suitable method for instance is exposing a sample either in a layer obtained from a hot melt or in a layer obtained by solvent coating to UV irradiation by passing said sample at a certain speed (expressed in meters per minute, m/min) underneath the UV source. If necessary, the exposure to irradiation may be repeated one or more times, e.g. by repeatedly passing the sample underneath the UV source or by passing the sample underneath two or more lamps positioned in series, in order to accomplish sufficient curing. The lower the total irradiation dose and the higher the speed with which the sample can be passed underneath the UV source for obtaining sufficient and satisfactory curing, the better the curing ability of the said sample. The UV curable block copolymer composition according to the present invention can be suitably applied in hot melt as well as solvent adhesive compositions, sealants and coatings. hen used in adhesive compositions, common additives, such as a tackifying resin, a softening oil and an antioxidant may also be present. For instance, a suitable hot melt adhesive composition may comprise in addition to the block copolymer composition of the present invention: (c) 10-300 parts by weight per 100 parts by weight of block copolymer (phr) of at least one resin which is compatible with the poly(conjugated diene) polymer block(s) ; (d) 0-150 phr of a plasticizer; and (e) 0.5-5 phr of an antioxidant. Suitable poly(conjugated diene) compatible resins are tackifying resins and liquid resins, such as e.g. polyterpene resins, polyindene resins, rosin esters, hydrogenated rosins, alpha-pinene resins, beta-pinene resins, hydrocarbon resins of petroleum origin and phenolic resins. Examples are REGALITE R91, R101, R 125 and S260 (REGALITE is a trade mark), ESCOREZ 1310 and 5380 (ESCOREZ is a trade mark) , WINGTACK 95 (WINGTACK is a trade mark), FORAL 85 and 105 (FORAL is a trade mark), PICCOLYTE A115, S115 and S10 (PICCOLYTE is a trade mark) and PICCOTAC 95E. The use of resins having a low degree of unsaturation, such as REGALITE R91, R101 or R 125, is preferred. As a plasticizer mineral oils, both naphthenic and paraffinic oils, or low molecular weight polybutylene polymers may be used. Examples of suitable plasticizers are SHELLFLEX 371 and 451 and TUFFLO 6204 (naphthenic oils), TUFFLO 6056 (paraffinic oil) and the polybutylenes HYVIS 200, NAPVIS 30 and NAPVIS D-10. SHELLFLEX, TUFFLO, HYVIS and NAPVIS are trade marks. Also very useful are REGALREZ 1018 (REGALREZ is a trademark) , ONDINA 68 (ONDINA is a trade mark) and V-OIL 7047 (V-OIL is a trade mark) . As component (e) any antioxidant commonly applied in adhesive formulations may be used. An example of such antioxidant is the phenolic compound IRGANOX 1010 (IRGANOX is a trade mark) . in addition to the components (c) , (d) and (e) other additives, such as endblock compatible resins, UV stabilizers, fillers, flame retarders and the like, may be present as well depending on the specific conditions under which the hot melt adhesive composition is to be used. Hot melt adhesive compositions, sealant compositions and coating compositions comprising the UV-curable block copolymer composition described hereinbefore also form part of the present invention. The same applies for cured compositions obtained by exposing said adhesive, sealant and coating compositions to UV irradiation. The invention is further illustrated by the following examples, however without restricting the scope of the invention to these specific embodiments. The photoinitiators used in the examples have been abbreviated as follows: TZT ESACURE TZT 1184 IRGACURE 184 XI5 ESACURE XI5 1651 IRGACURE 651 P115 UVECRYL P115 1907 IRGACURE 907 UVEC UVECRYL 7100 Benz Benzophenone Unless otherwise mentioned, the samples were irradiated by a UV source while being exposed to a soft flow of nitrogen. This flow of nitrogen was such that oxygen was still present during irradiation. Accordingly, irradiation took place in the presence of up to.10 volume % of oxygen. Example 1 A formulation consisting of a multi-armed S-I block copolymer, two polyisoprene compatible resins and an antioxidant was prepared by intimately mixing: 100 pbw of KRATON D-1320X, 150 phr REGALITE R91, 60 phr REGALREZ 1018, and 1 phr IRGANOX 1010. KRATON D-1320X is a multi-armed block copolymer consisting of S-I block copolymer arms. The coupling agent used is divinylbenzene. It has a polystyrene content of 10% by weight. The apparent molecular weight of each S-I arm is about 100,000 and the peak molecular weight of each polystyrene block is about 11,000. The total number of arms may vary from 6 to 100 and usually is between 6 and 40. To this formulation several photoinitiators were added after which the compositions thus obtained were exposed to UV irradiation by passing the formulation as a hot melt underneath a single Fusion D bulb lamp (F300; 300 W/inch) at a speed of 5 m/min. Of these compositions the Shear Adhesion Failure Temperature (SAFT) was measured. A value of 140 °C or higher is acceptable. The results are listed in Table I. TABLE I UV curing of several formulations photoinitiator (pbw) TZT X15 1651 1184 UVEC SAFT (°C) 1 pass 2 passes 5 110 >160 10 >160 >160 5 114 >160 10 >160 >160 3 10 >160 >160 5 151 >160 3 137 140 5 10 >160 >160 10 10 >160 >160 From table I it is clear that all formulations show excellent SAFT values after 2 passes underneath the D bulb UV lamp, (300 W/inch) while five formulations already give excellent SAFT values, i.e. >160 °C, after only 1 pass. Example 2 The same base formulation as used in Example 1 was employed for the evaluation of the effect on the SAFT values of the speed with which a formulation is passed underneath various UV sources. The photoinitiator used was IRGACURE 907 in an amount of 5 pbw per 100 pbw of block copolymer. When two bulb lamps were positioned in series (indicated as D+V, D+H and D+D), the exposure to the irradiation originating from the second lamp took place in air, so without applying a nitrogen flow. The results are listed in table II; the SAFT values listed are given in °C. TABLE II SAFT values after UV curing at different speeds and with different UV lamps Speed D bulb D+H bulb D+V bulb D+D bulb (m/min) 1 pass 2 passes 1 pass 1 pass 1 pass 5 >160 >160 >160 >160 >160 10 112 >160 >160 >160 123 15 104 131 >160 118 105 20 97 106 156 104 98 The H and V bulb had a linear power of 300 W/inch (120 W/cm) From table II it is clear that particularly the combination of a D bulb lamp followed by a H bulb lamp gives excellent results, even at such high speed as 20 m/min. Characteristic adhesive properties (loop tack and peel adhesion) were also measured of same irradiated samples as listed in Tables III and IV. TABLE III Looptack: Influence of the lamp and speed (N/25mm) Speed D-Bulb (1 lamp) D+H Bulb D+D Bulb M./Min. 1 pass 2 passes 1 pass 1 pass with without with without with with without * 5 26 28 26 25 2 233 2 211 21 10 27 - 25 21 26 * * 15 25 26 24 24* 26 22 * 20 25 _ 22 23 24 'with' : means with low N„ flow - 'without' : means that the samples wweerree ccuurreedd iinn oopen atmosphere (no N_ flow) *: zippery tack TABLE IV Peel adhesion: Influence of the lamp and speed (N/25mm) Speed D-Bulb (1 lamp) D+H Bulb D+D Bulb M./Min. 1 pass 2 passes 1 pass 1 pass with without with without with with without 5 19 19 16 17 1 177 1 199 19 * 10 20 18 17 19 15 17 19 19 18 16 17 20 16 20 - 21 19 From these tables it will be appreciated that the adhesive properties are not damaged by the curing. Example 3 The same formulation as used in Example 2 was employed and exposed to irradiation using a Fusion H bulb lamp (F300) with and without a nitrogen flow. The formulation was exposed to irradiation by passing it at different speeds once and twice underneath the H bulb as well as by passing it once underneath two H bulb lamps positioned in series. The SAFT values (in °C) were measured after each pass. The results are listed in table V. TABLE V SAFT values after UV curing with and without nitrogen flow Speed 1 lamp 2 lamps (m/min) 1 pass 2 passes 1 pass with without with without without 5 173 166 174 169 172 10 146 159 160 159 155 15 106 108 137 152 167 20 88 85 107 101 117 From table V it can be derived that irradiation in air, so without applying a nitrogen flow, results in excellent SAFT values which are similar to, and in some cases even better than, the SAFT values obtained by applying a nitrogen flow during exposure to irradiation. Example 4 Several photoinitiators and combinations of photoinitiators were added to the base formulation as used in Example 1. The compositions thus obtained (compositions A to G) were cured by passing them three times (lp, 2p, 3p) at a speed of 5 m/min underneath a Fusion D bulb lamp. The SAFT values, of some compositions the Holding Power at 95 "C (HP 95°C) and the peel adhesion 180° were determined after each pass. The results are listed in table VI. TABLE VI UV curing of block copolymer compositions Composition A B C D E F G Benz 5 5 10 10 5 10 1651 5 5 UVEC 10 P115 10 1907 5 ip 150 148 157 133 155 >160 141 SAFT (°C) 2p >160 >160 158 >160 >160 >160 147 3p >160 >160 159 >160 >160 >160 151 ip >100 >100 >100 >100 >100 HP 95°C 2p >100 >100 >100 >100 >100 3p >100 >100 >100 >100 >100 Peel- ip 20 18 16 19 16 16 10 adh. 180° 2p 18 20 21 21 16 15 12 (N/25mm) 3p 21 20 18 22 17 16 13 From table VI it can be seen that in particular the UV cured adhesive compositions A to F exhibit excellent adhesive properties. Example 5 A formulation, comprising: KRATON D-1320 X 100 phr REGALITE R 91 150 phr REGALREZ 1018 60 phr IRGACURE 907 5 phr IRGANOX 1010 1 phr was tested with irradiation from another UV-lamp, the H-bulb, which substantially emits the conventional mercury spectrum. The SAFT test results obtained have been listed in Table VII: Table VII SAFT: Influence of the H-bulb lamp (°C) Speed 1 Lamp 2 Lamps M./Min. 1 pass 2 passes 1 pass with without with without without 5 171 167 171 169 168 10 145 148 164 155 147 >160 >160 15 99 107 137 152 >160 20 88 85 107 101 112 From this table VII it will be appreciated that the N. is not necessary and has hardly any influence on the curing efficiency of this formulation. Moreover it appeared possible to have a good curing efficiency with two passes under the H-lamp up to 15 m/min (SAFT higher than 150 °C) . The adhesive properties of these samples have also been measured and listed in Tables VIII and IX. Table VIII LOOPTACK: Influence of the H-bulb lamp (N/25mm) Speed 1 Lamp 2 Lamps M./Min. 1 pass 2 passes 1 pass with without 1with without without * 5 25 23 15 18 21 10 24 25 24 24 21 15 24 23 23 25 23 * * 20 23 20 20 20 21 * = zippery tack TABLE IX Peel adhesion: Influence of the H-bulb lamp (N/25mm) Speed 1 Lamp 2 Lamps M./Min. 1 pass 2 passes 1 pass with without with without without 5 20 20 17 18 16 10 18 18 17 18 16 15 19 20 16 16 19 20 19 21 20 22 19 From the previous results it will be appreciated that the adhesive properties are not damaged by the curing whatever the curing speed or dose. Example 6 A similar formulation (KRATON D-1320X/REGALITE R91/REGALREZ 1018/IRGAN0X 1010;100/150/60/1) was used with a combination of benzophenon and EBECRYL 7100 (or UVECRYL 7100: both trade names exist for the same product) as photoinitiator. The samples were irradiated under a H-bulb at different speeds. The temperature resistance results (SAFT and Holding Power 95 °C) have been listed in Tables X and XI: TABLE X SAFT: Influence of curing speed (°C) Adjusted components benz. EBECRYL 5 m./min. 10 m. /min . 15 m. /min . 20 m . /min . 1 p 2 p l p 2 p l p 2 p l p 2 p 10 10 156 163 154 158 92 159 111 130 10 155 169 159 97 105 95 108 ' * = zippery tack TABLE XI HP 95 °C: Influence of curing speed (h) Adjusted components benz. EBECRYL 5 m./min 10 m./min 15 m./min 20 m./min 500 g 1 kg 500 g 1 kg 500 g 1 kg 500 g 1 kg 10 10 1 P > 100 6 0.07 2 P > 100 61 > 100 77 15 From these data it will be clear that also good curing efficiency was obtained in open air with a combination of benzophenon and tertiary amine as photoiniator. Example 7 1. Two radiation curable block copolymer mixtures (A and B) of molecular structure (SB) B X, wherein m + n - 4, and each of m and m n n had an average value of about 2, wherein X represented the residue of tetrachlorosilane, were tested in an "open air" irradiation process with two photoinitiators covered by the present application, i.e. IRGACURE 651 and IRGACURE 907 respectively. Further details of these polymers have been listed in Table XII. TABLE XII Polymer % PS 12.7 10.8 % vinyl 54 56 CE 96 95 T ■ 59 °C •56 °C g MFR 8.1 1.4 Adhesive Composition (3) (4) (5) (6) polymer 100 phr 100 REGALITE 91 147 129 REGALEZ 1018 63 81 IRGACURE 651 IRGACURE 907 IRGANOX 1010 The samples were cured at different speeds, under a F-300 D-bulb lamp. These adhesive formulations were irradiated in direct cure, with low N~ flow. The results have been listed in Table XIII. TABLE XIII Speed Composition (3) Composition (4) Composition (5) Composition (6) m./min. 1 p 2 p 1 p 2 p 1 P 2 p 1 P 2 p 5 > 160 135 > 170 > 170 > 170 > 170 > 160 > 160 10 79 80 81 > 160 89 > 160 85 96 15 69 75 76 86 84 86 75 75 20 72 74 78 81 83 81 74 77 O 2. The experimental polymers A and B of the formula (SB^B^X were then cured with a more powerful lamp at higher speeds, without any nitrogen flow. The photoinitiators IRGACURE 651 and 907 were both tested in compositions, containing the same other ingredients as specified in Table XII, i.e. formulation 4 is based on A oolymer with IRGACURE 651, formulation 5 is based on B polymer with IRGACURE 651, formulation 6 is based on B with IRGACURE 907. All the samples were irradiated in direct curing by means of Fusion F-600 lamps. The results have been listed in Tables XIV and XV. TABLE XIV Speed D-bulb H-bulb m./min 4 5 6 4 5 6 0 75 80 75 80 10 >170 >170 >170 >170 >170 >170 20 77 >170 >170 170 >170 >170 25 90 153 >170 166 >170 >170 30 80 105 >170 95 >170 >170 40 74 86 141 86 118 >170 50 76 86 95 77 92 127 SAFT results (°C) for samples cured under one F-600 lamp TABLE XV Speed D + D bulb D + H bulb m./min 4 5 4 5 6 0 75 80 75 80 20 >170 >170 >170 >170 >170 30 >170 >170 150 >170 >170 40 111 >170 106 147 >170 50 82 114 86 >170 >170 60 80 110 84 >170 >170 SAFT results (°C) for samples cured under a combination of F-600 lamps It will be appreciated that improved results were obtained, when using the IRGACURE 907 photoinitiators. The best results were obtained for a B polymer based formulation irradiated by a combination of D and H bulbs. In this case, SAFT results higher than 170 °C could be obtained at a speed of 60 m./min! This is the highest speed which ever could be reached in radiation curing. Holding Power (HP) at 95 °C:1 kg. Only the samples which had good temperature resistance properties were selected to perform a HP 95 °C test, as listed in Table XVI. TABLE XVI Speed D-bulb H-bulb m./min 4 (h) 5 (h) 6 (h) 4 (h) 5 (h) 6 (h) 10 >100 >100 >100 >100 >100 >100 20 - >100 >100 0.5/12.5 >100 >100 25 - - >100 0/42 9.5/>100 >100 30 - - >100 0 >100 >100 40 - - - - - 8.6 HP 95 °C results of samples cured under one F-600 lamp TABLE XVII Speed D + D bulbs D + H bulbs m./min 4 (h) 5 (h) 4 (h) 5 (h) 6 (h) 20 >100 >100 >100 >100 >100 30 >100 >100 19/>100 >100 >100 40 - >100 - >100 >100 50 - - - >100 >100 60 - - - >100 >100 HP 95 °C results of samples cured under a combination of F-600 lamps Here again we can see the good temperature performance (HP95 °C > 100 h) of the experimental polymers when using IRGACURE 907 photoinitiator. IRGACURE 907 enabled the achievement of higher curing speeds. From the preceding examples it will be appreciated that it became possible to effectively cure in presence of oxygen without the need of a N. flow. High curing efficiency and temperature resistance properties achievable at high speed could be reached. Example 8 (i) Five standard radiation sensitive compositions were prepared, comprising 100 parts by weight of each of the block copolymers containing poly(styrene) and poly(butadiene) blocks, listed in Table XVIII, 1 part by weight of the antioxidant IRGANOX 1010 and 2 parts by weight of photosensitizer IRGACURE 651. The last block copolymer listed in the table is not according to the claimed invention and has been included as comparative example. TABLE XVIII Polymer characteristics Block Mol.wt. Mol.wt. Total mol.wt. Molecular Poly- Vinyl- Copolymer (xlOOO) (xlOOO) (xlOOO) form styrene (1,2-add) of S of S-B content content block block A 10.7 71 276 (SB) 2 B 2 12.7 54 B 11.2 87 339 (SB) 2 B 2 10.8 56 C 10.7 81 222 (SB) 2 B 2 12.5 60.5 KRATON D 13 330 21 +/- 5 (SB) 3.5 1116 Comp. 12 45 91 SBS 40 +/- 5 From the five photosensitive compositions films of 22 micron thickness were prepared from a solvent based formulation (40% in toluene) by casting. The films were irradiated under a Fusion D bulb lamp in 1 pass and 2 passes respectively with a speed of 5 m/min, and the gel content was analyzed. The gel contents have been listed in Table XIX. TABLE XIX Gel percentage after irradiation Polymer 1 pass 2 passes A 59.5 85.5 B 81.0 86.9 C 73.8 87.5 KRATON D 1116 31.7 70.4 Comp. 0.3 9.6 (ii) Photosensitive compositions were prepared from the block copolymer identified hereinbefore as A (100 parts by weight) , IRGANOX 1010 (1 part by weight) and varying amounts of photosensitizer IRGACURE 651, as listed in the Table XX. Films of 22 micron thickness were prepared from these compositions and the films were irradiated as described under Example 8(i) . The percentage .gel after irradiation was determined. TABLE XX % gel after irradiation Composition block Copol./AO/PS 1 pass 2 passes 100/1/1 46.2 73.3 100/1/2 59.5 85.5 100/1/4 . 84.7 93.7

Claims: C L A I M S 1. UV-curable block copolymer composition comprising: (a) 100 parts by weight of a block copolymer comprising at least one polymer block A derived from a monovinyl aromatic compound and at least one polymer block B derived from a conjugated diene, wherein: the content of monovinyl aromatic compound is in the range of from 5 to 50% by weight based on the total weight of block copolymer; each block A has an apparent molecular weight in the ° range of from 1,000 to 50,000; and each block B has an apparent molecular weight in the range of from 10,000 to 250,000; and (b) 0.5-30 parts by weight of at least one photoinitiator, characterized in that the block copolymer is a multi-armed block 5 copolymer and at least one photoinitiator is used containing a carbonyl group which is directly bonded to at least one aromatic ring strueture. 2. Composition according to claim 1, characterized in that the multi-armed block copolymer has a content of monovinyl aromatic 0 compound in the range of from 5 to 25% by weight. 3. Composition according to claim 1 or 2, characterized in that the block copolymer has the general formula (A-B) X, wherein n is an integer in the range of from 3 to 20 and X is a coupling agent residue. 5 4. Composition according to any one of claims 1 to 3, characterized in that the monovinyl aromatic compound is styrene and the conjugated diene is isoprene, 1,3-butadiene or a mixture thereof. 5. Composition according to claim 4, characterized in that the 0 conjugated diene is isoprene. 6. Composition according to any one of claims 1 to 5, characterized in that component (b) contains at least one photoinitiator selected from the group consisting of: (1) at least one benzophenone of the general formula (I) 1 8 wherein R to R independently represent hydrogen or an alkyl 7 8 group having from 1 to 4 carbon atoms and wherein R and or R represent in addition alkoxy of 1 to 4 carbon atoms and wherein n has a value of 0,1 or 2, optionally in combination with at least one tertiary amine, (2) at least one sulphur-containing carbonyl compound, wherein the carbonyl group is directly bound to at least one aromatic ring, preferably of the formula II , and (3) mixtures of (1) and (2). 7. Composition according to claim 6, wherein the photoinitiator is selected from the group consisting of benzophenone, a mixture of benzophenone and a tertiary amine, 2,4,6-trimethylbenzophenone, 4-methylbenzophenone, 2,2-dimethoxy-l,2-diphenylethan-l-one, and 2-methyl-l- [4-(methylthio)phenyl] -2-morpholinopropanone-l»and mixtures thereof. 8. Composition according to claim 7, wherein the photoinitiator is 2-methyl-l- [4-(methylthio)phenyl]-2-morpholinopropanone-l. 9. A hot melt adhesive composition comprising the block copolymer composition according to any one of claims 1 to 8. 10. A sealant composition comprising the block copolymer composition according to any one of claims 1 to 8. 11. A coating composition comprising the block copolymer composition according to any one of claims 1 to 8. 12. A process for the curing of the compositions according to any one of claims 9-11 by exposing said compositions to UV irradiation in the presence of air. 13. A cured composition obtainable by the process of claim 12.

Inventors: DE KEYZER NOEL RAYMOND MAURICE, DUPONT MARTINE JEANNE, MORREN KARIN MARIE-LOUISE RENE, DE KEYZER, NOEL, RAYMOND, MAURICE, DUPONT, MARTINE, JEANNE, MORREN, KARIN, MARIE-LOUISE, RENEE
Applicants: SHELL INT RESEARCH, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1994
Main classification: C08L53
IPC codes: C08F2, C08F299, C08K5, C08L53, C09D153, C09J153